The game has its own unique story elements, and the way you access the Gym in Saffron City differs from the original games. Here's how it works:
* Talk to Sabrina: Instead of using a card key, you'll need to talk to Sabrina, the Gym Leader, herself. You'll find her in the Gym, and she'll give you access to the Gym and allow you to challenge her.
This is a unique change in Pokemon Liquid Crystal, making the game more engaging and different from the original.